I've been having a good time killing those flying reptiles with magic in the valley and desert. If you want to give it a try, here's some tips and techniques I used to bring them down to earth.
First make sure your heath is full because you're gonna get bit a few times before you can fight back. Make sure you have a spell selected before you start your attack too. When you first get off Arokh you're empty handed. I've been guilty of trying for a target lock with low health and no spell. Duhhh!
The most important tip is to become a tree hugger. The trunk will protect you from a frontal attack and the branches will cover the overhead blasts. The best tree is one that's close to a hill or the base of a cliff to cover your back. It forces the dragon to attack from the front or side. With the right tree you can fight two at the same time.
You'll have to get proficient at strafing around the tree manually to avoid attacks from the back and sides as the dragon strafes you. As you're strafing around the tree, use the right stick to point up/right/left at the dragon to get target lock when it gets close enough, which is PRETTY CLOSE. Look it right in the face using the left and right sticks. You'll have to learn how to do a little 'tree dance'. It can be a bit tricky to learn but it's not too bad after you get the hang of it.
Once you have your tree picked out (from a distance) you may have to run for it if you trigger the dragon. Use stealth and natural cover to get there with as little damage as possible. Keep your eyes on the dragon and if he moves toward you, RUN like the wind!
If you get there without triggering it, use Lightning or Fireball to attract it's attention. Strafe out from behind the tree to get a clear shot. Use the top Rynn's head as your sight and the right stick for the elevation. Turn and strafe in little amounts to fine tune your aim. Lightning self targets and it's easier to use but sometimes it won't reach the dragon due to the landscape. Fireball is a bit harder to aim but it may be the only way to trigger it.
The spells I used the most were Lightning, Fireball, Soul Steal, and Combust in about that order. You'll probably have to strafe out a little from the tree to get a shot off depending on the landscape. Make your moves quickly to avoid damage. Soul Steal may 'tame' the dragon a bit and make it become sluggish and just hang in the same spot. Try to avoid splash damage to yourself if you use Fireball.
Don't use Combust on Bone Dragons, it has no effect. It works well on fleshy dragons though. Don't use Impale either. I have not been able to get a target lock with it. It seems the enemy must be on the ground for that spell to work. I really wanted to take a dragon for a spin too. Drats.
That should get you started on your hunt. If you're going through the game as a Mage, you owe it to yourself to try to pick off a few dragons. It's frustrating and fun at the same time. I've killed all the Bone Dragons in the desert using these techniques, Tora and Shazzar are next. I invite you to become a member of the Desert Dragon Hunt Club.